In the IP (Internet Protocol), a subnetwork-only broadcast called a local broadcast, and a network-wide broadcast are defined. In order to avoid unnecessary traffic and achieve security, a router is configured to prevent the network-wide broadcast from going out of a subnetwork. However, it may happen that a broadcast generated in a predetermined subnetwork should desirably be notified to a predetermined external subnetwork.
Background Art 1
In the case where subnetworks A1 and A2 included in a network adopting DHCP (Dynamic Host Configuration Protocol) are a subnetwork having no DHCP server therein and a subnetwork having a DHCP server therein, respectively, when a DHCP client in the subnetwork A1 outputs a network-wide broadcast (255. 255. 255. 255) inside the subnetwork A1 for the sake of requesting an IP address, a DHCP relay agent in the subnetwork A1 changes the address of the IP packet related to the network-wide broadcast to the address of the DHCP server in the subnetwork A2 and outputs it to the subnetwork A1 so that the packet will reach the DHCP server in the subnetwork A2.
Background Art 2
In a network including an IBM Director server and an IBM Director broadcast relay agent, the server outputs to a subnetwork B1 a packet having a destination address which is the one of the broadcast relay agent in a subnetwork B2 different from the subnetwork B1 to which the server belongs. Upon receiving the packet, the broadcast relay agent in the subnetwork B2 outputs a broadcast for the subnetwork B2 to the subnetwork B2.
Problems of the background art 1 are as follows.    (1) Among the broadcasts generated in the subnetwork A1, it is only a DHCP broadcast that has its contents notified to another subnetwork A2.    (2) The DHCP server in the subnetwork A2 only uses a unicast received from the DHCP relay agent in the subnetwork A1 for the sake of its own processing, and any host in the subnetwork A2 is not informed of the contents of broadcast in the subnetwork A1.
Problems of the background art 2 are as follows.    (1) The IBM Director server in the subnetwork B1 only sends a notice of broadcast for the subnetwork B2 to the broadcast relay agent in the subnetwork B2 for its own use, and the contents of network-wide broadcast generated by any host in the subnetwork B1 are not notified to the subnetwork B2.    (2) For a network-wide broadcast generated by any host in the subnetwork B1, its contents are not notified to any host in the subnetwork B2.    (3) Any host belonging to the subnetwork B1 other than the IBM Director server must know the existence and address of the broadcast relay agent in advance to pass a broadcast to the subnetwork B2 via the broadcast relay agent.